A digital storage oscilloscope (DSO) is the primary tool utilized by engineers to view electrical signals. As signals get ever faster, it is very beneficial to have DSOs capable of digitizing, displaying and analyzing these faster signals. The capability of a DSO to digitize fast signals is determined by its bandwidth and sample rate.
Because one of the uses of the DSO is to design and analyze new electronic devices, DSOs employed in the design of high speed electronics must operate at a bandwidth sufficient to capture and display signals from these devices. Providing ever-faster sampling circuitry is one way to increase bandwidth, but is subject to practical limitations in hardware development. There are a number of other methods that have been traditionally employed in an attempt to provide additional bandwidth. One of the more common methods is called equivalent time sampling and is based upon triggering repeatedly on a periodic event. Data from multiple trigger events can be combined to provide a more complete and accurate view of the waveform. This technique is employed in a conventional sampling oscilloscope. A sampling oscilloscope repeatedly triggers on an event and acquires only a few points of the periodically repeating waveform (sometimes only one point of the waveform) in response to each trigger event. After repeated triggers, the acquired data points are combined to display a high effective sampling rate representation of the waveform. However, such a sampling oscilloscope requires a repetitive input signal so that the representation of the waveform can be generated over many triggers. This method also makes certain desirable types of analyses of the waveform, such as cycle-to-cycle jitter, impossible.
A common problem in complex signal analysis is that a non-repetitive signal must be analyzed. In fact, it is very often the case that a non-repetitive event is the cause of some failure in an electronic system. It is the function of the test equipment to help the user identify the cause of the failure. Therefore, a piece of test equipment that requires repetitive signals may be of limited usefulness. Situations when the user wants to capture or look at infrequent or non-repetitive events require a DSO capable of operating with high bandwidth and sample rate in response to a single trigger. Such a DSO that allows for acquisition of a signal based upon only a single trigger event is called a real-time oscilloscope. Acquisitions taken utilizing only a single trigger event are called single-shot acquisitions.
While architectural techniques, such as channel combination, interleaving, and the like are generally available for designing high sample rate real time oscilloscopes, designing real time oscilloscopes that simultaneously achieve high bandwidth and high sample rate is another issue. Increasing bandwidth in such a real time oscilloscope is typically dealt with through direct application of ever faster, very good high-speed electronics. Increasing the sample rate is generally achieved by the application of various interleaving techniques. As noted above, a real-time DSO is more useful in certain situations than a sampling oscilloscope, even though a sampling oscilloscope provides high bandwidth and effective sampling rate. This is because unlike a sampling oscilloscope, a real time DSO does not require the input signal to be repetitive. However, in order to allow for acquisition of enough sampling points in real time to accurately reproduce the acquired signal, the bandwidth of the real-time scope may be limited.
Even with current design techniques it is difficult to achieve simultaneously very high bandwidths and sampling rates.